Abstract: Objective: To compare the stability of two kinds of micro-screw system placed in maxillary posterior area. Methods: 102 patients were selected with 176 micro-screws placed. Possible influencing factors including the kinds of micro-screws, age and skeletal patterns were analyzed by Chi-square tests through SPSS Statistical Package. Results: Different kinds of micro-screws and different skeletal patterns exhibited significantly different failure rates (P<0.05). No significant difference was found between age groups. Conclusion: Higher failure rates were conformed in group of stainless steel micro-screws compared with Ti-alloy micro-screws. The failure rates in high angle cases were higher than those of lower and average angle cases.